Quantum Conundrum is a wacky Portal-like puzzle game centered around a weird science contraption that switches dimensions. It's whimsical, fun, well made, well written, it controls well, and it's a blast to play. It's almost flawless. The puzzles are made up of simple elements that are combined into complicated and elaborate puzzles.
It's too good for a $15 downloadable title. I almost didn't believe it when I looked at the price; I felt like I was playing a $50 game. I simply can't recommend this game enough. In fact, you are an idiot if you don't buy Quantum Conundrum.